Investigation of nuclear-medium effects on elementary-particle reactions at the synchrotron COSY in Jülich

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The objection of the joint research project will investigate the influence of the nuclear medium on reactions among nucleons. Proton-induced processes in target nuclei will be studied at internal targets with the 0 degree Facility of the Cooler Synchrotron "COSY" at the Forschungs-zentrum Jülich in Germany, where high-precision beams are available. The use of internal targets avoids problems with energy losses of projectiles and ejectiles as well as background from window materials. Polarised gas targets can be used for the study of spin observables.

The first investigations are: inclusive and exclusive measurements of the double differential cross sections for the K+ production below the free-nucleon-nucleon threshold. The mechanism of the production process, high-momentum components of the nuclear wave function as well as the participation of correlated groups of nucleons will be investigated; and a study of the deuteron break-up reaction using a (1-2.5 GeV) polarised proton beam and polarised deuterium gas target. Vector and tensor analysing powers, and spin-correlation asymmetry will be exclusively measured in a special geometry, where the slow, backward emitted proton is detected in coincidence with the fast forward projectile proton. In such a geometry, the deuteron S-state and D-state wave functions will be investigated up to internal momenta of 0.5 GeV/q.

For these studies, dedicated complex detection systems will be developed. The NIS members of the collaboration will build part of these detectors and contribute to the preparation of other components of the experimental set-up, especially of the polarised target.